The verification phase is becoming the norm for confirming VO 2max during a graded exercise test (GXT), but the use of such testing in untrained participants in the heat remains unknown. Purpose: This study aimed to assess the VO 2 uptake obtained during a GXT and subsequent verification phase in untrained participants in a hot environment. Methods: Twelve sedentary males completed a GXT followed by a biphasic supramaximal-load verification phase in a hot environment (39°C, 32% relative humidity). Rest between tests occurred in a temperate chamber and lasted until gastrointestinal temperature returned to baseline. Results: Mean verification phase VO 2max (37.8 ± 4.3 mL•kg −1 •min −1 ) was lower than GXT (39.8 ± 4.1 mL•kg −1 •min −1 ; P = 0.03) and not statistically equivalent. Using an individualized analysis approach, only 17% (2/12) of participants achieved a VO 2 plateau during the GXT. Verification phase confirmed GXT VO 2max in 100% of participants, whereas the traditional and the new age-dependent secondary VO 2max criteria indicated GXT VO 2max achievement at much lower rates (8/12 [67%] vs 7/12 [58%], respectively). Correlational indices between GXT and verification phase VO 2max were strong (intraclass correlation coefficient = 0.95, r = 0.86), and Bland-Altman analysis revealed a low mean bias of −2.1 ± 1.9 mL•kg −1 •min −1 and 95% limits of agreement (−5.8 to 1.7 mL•kg −1 •min −1 ). Conclusions: Very few untrained males achieved a VO 2 plateau during GXT in the heat. When conducting GXT in a hot condition, the verification phase remains a valuable addition to confirm VO 2max in untrained males.
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